The plumber omitted to fit an AAV when installing our ensuite - probably because of difficulty of access.. I dont think its possible to fit a 110mm AAV because of lack of space but there is room to get some 32mm pipe connected. The question is will a 32mm AAV work satifactorily if it is connected to a 110mm waste system?

providing you have 2 independant connections to the soil stack it is possible to use HepVo traps in place of conventional traps with no requirement for an air admittance valve provided other properties in the area (1in 10) has conventional vent stack and your property is not on a septic tank. This method comforms with building regulations.